A retrofit device to resist torque while a compression metal face seal is tightened.
Metal face seals are widely used in critical piping areas where utmost purity and protection of the confined gases, and security against leakage of what are often extremely toxic gases are critical. Essentially these face seals involve pressing a circular metal ring-shaped face seal against a metal gasket. They are compressed against and slightly indented into the contiguous gasket surface, by tightening a female internally threaded nut onto an externally threaded male nut. Shoulders on the nuts press the face seals (or more specifically the heads which bear the face seals) against the gasket when the nuts are tightened.
So long as the face seals experience only axial compressive forces, the face seals will simply engage and detent somewhat into the gasket. The very accurate shape and fine finish of the face seals are not damaged.
However, should there be a twisting movement of one relative to the other while they are being pressed against a contiguous surface, and especially if that surface is the other face seal, the face seals can be damaged, often so badly that they could leak, and they must then be replaced. Replacement in installations such as are used in semiconductor manufacture can be very costly both in labor and equipment, and in down time for the apparatus. Unless precautions are taken, such twisting movement can be caused by the nuts, when one engages a respective head and rotates the heads and face seals relative to the other, even slightly.
This is not a new problem. Three previous patents have addressed the same general problem. These are:
McGushion U.S. Pat. Nos. 5,054,822 and 5,306,052
Robinson U.S. Pat. No. 5,829,796
In these patents, which show products that are in use today, the products relate to joining the seal-bearing heads of two manipulable lengths of tubing. None, however, attends to the common situation where one of the nuts and its associated head and face seal are not readily accessible for the use of a torque-resisting system.
An example is an outlet fitting on a bulkhead connectors, filters, mass flow controllers and some valves, in which the fitting, which is already fixed on the component or valve, is simply a male nut with a face seal on its end. Then, when the female nut is applied along with its associated face seal and gasket, rotation of the nut can cause limited rotation of the face seals, and can damage one or both of the seals.
It is an object of this invention to provide a retrofit attachment for the male nut which can separately be attached to an existing, already installed male nut that will provide torque-limiting blades which can be engaged by matching torque limiting blades pressed by the female nut against one of the heads, thereby preventing relative rotation of the face seals.
A retrofit fitting according to this invention is intended to be threaded onto an already installed male nut, which male nut itself carries a face seal to be abutted and protected against rotational contact with an engaging gasket. A second face seal is pressed against the other side of the gasket by a threaded nut. The fitting also protects the face seals from contacting each other.
According to this invention, the retrofit fitting is a tubular adaptor threaded both internally and externally, and which carries a pair of torque-resisting blades. When the retrofit fitting is tightly threaded onto the male nut, it in effect becomes a non-rotating portion of the male nut, and provides torque-resisting blades.
A torque cage includes a complementary set of blades which engage the blades of the retrofit fitting. The female nut surrounds and turns against the cage as it drives it axially, but this torque is isolated from the second face seal by the blades so it cannot be turned.
This arrangement thereby provides an easily-applied retrofit fitting which enables the face seals on two heads to be restrained against relative rotation while the two nuts are threaded together.